Thermoplastic molding materials based on highly effective grafted rubber components

ABSTRACT

The invention provides thermoplastic molding compositions of the ABS type containing highly effective graft rubber components obtained by emulsion polymerization while using a special initiator system and maintaining defined reaction conditions.

The invention provides thermoplastic moulding compositions of the ABStype containing highly effective graft rubber components obtained byemulsion polymerisation while using special initiator systems andobserving defined reaction conditions.

Moulding compositions of the ABS type are two-phase plastics materialsconsisting of

I) a thermoplastic copolymer of styrene and acrylonitrile in which thestyrene can be replaced completely or partially by α-methyl styrene ormethyl methacrylate; this copolymer, also known as SAN resin or matrixresin, forms the external phase;

II) at least one graft polymer produced by graft reaction of one or moreof the monomers mentioned under I on butadiene—homo—or copolymer (“graftbase”). This graft polymer (“elastomer phase” or “graft rubber”) formsthe dispersed phase in the matrix resin.

With an identical matrix, the viscosity of an ABS moulding compositionis determined substantially by the graft rubber. However, the viscosityrequired for markedly stressed mouldings cannot always be achieved withthe necessary reliability using conventional ABS moulding compositions,particularly if very high viscosities are demanded at low temperaturesor if these requirements are met only at the cost of other propertiesalso required, for example rigidity or processing behaviour.

There is therefore a need for graft rubbers on the basis of which ABSmoulding compositions with very high viscosities at room temperature andat low temperature can be produced without impairing the otherproperties, in particular rigidity and processibility.

Furthermore, it should also be possible to produce these graft rubberson the basis of more finely divided rubber bases so that mouldings withhigh surface lustre can also be obtained if necessary.

It has accordingly been found that moulding compositions of the ABS typewith excellent viscosities at room temperature and low temperature areobtained without adversely affecting the other properties if the graftrubber employed is produced while using special combinations ofinitiator systems and while maintaining defined reaction conditions.

The production of graft rubbers using various initiator systems isknown. Thus, numerous documents, for example EP-A 154 244, describe theuse of potassium persulfate as initiator. Documents such as, forexample, EP-A 745 623 (see also the literature quoted therein) describethe use of special redox systems or of azo initiators. Althoughinitiator systems of this type lead to graft polymers which lead to goodproperties in thermoplastic moulding compositions for specialrequirements, good viscosities at high and low temperatures are notachieved to the adequate extent while maintaining the other properties.

The invention provides thermoplastic moulding compositions of the ABStype containing

A) at least one elastic/thermoplastic graft polymer obtained by radicalemulsion polymerisation of resin-forming vinyl monomers, preferably ofstyrene or acrylonitrile, wherein styrene and/or acrylonitrile can becompletely or partially replaced by α-methyl styrene, methylmethacrylate or N-phenylmaleimide, in the presence of rubber existing inlatex form with a glass transition temperature ≦0° using an initiatorcombination consisting of a redox initiator system and a persulfatecompound and

B) at least one copolymer of styrene and acrylonitrile, wherein styreneand/or acrylonitrile can be completely or partially replaced by α-methylstyrene or methyl methacrylate or N-phenylmaleimide,

characterised in that the graft polymer A) is produced by supplying themonomers to the rubber latex, the redox initiator components are addedat the beginning of the graft polymerisation reaction in quantities of0.1 to 2.5 wt. %, preferably of 0.2 to 2.0 wt. % and particularlypreferably of 0.5 to 1.5 wt. % (based on the monomers added up to themoment of addition of persulfate compound in each case), a persulfatecompound is added after an addition of monomers of 10 to 95 wt. %,preferably 20 to 85 wt. %, in particular 20 to 80 wt. % particularlypreferably 30 to 75 wt. % and quite particularly preferably 35 to 70 wt.% (based on total quantity of monomer in each case), in quantities of0.05 to 1.5 wt. %, preferably of 0.08 to 1.2 wt. % and particularlypreferably of 0.1 to 1.0 wt. % (based on the monomers added from themoment of addition of persulfate compound in each case) andpolymerisation is carried out until completion.

In principle, any rubber-like polymers existing in the form of anemulsion with a glass transition temperature lower than 0° C. aresuitable as rubbers for producing the elastic/thermoplastic graftpolymers according to the invention.

Examples of suitable polymers include

diene rubbers, i.e. homopolymers of conjugate dienes containing 4 to 8carbon atoms such as butadiene, isoprene, chloroprene or copolymersthereof with up to 60 wt. %, preferably up to 30 wt. % of a vinylmonomer, for example acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, halogen styrenes, C₁-C₄ alkyl styrenes, C₁-C₈ alkyl acrylates,C₁-C₈ alkyl methacrylates, alkyleneglycol diacrylates, alkyleneglycoldimethacrylates, divinyl benzene;

acrylate rubbers, i.e. homo- and copolymers of C₁-C₁₀ alkyl acrylates,for example homopolymers of ethyl acrylate, butyl acrylate or copolymerscontaining up to 40 wt. %, preferably not more than 10 wt. % ofmonovinyl monomers, for example styrene, acrylonitrile, vinylbutylether,acrylic acid (ester), methacrylic acid (ester), vinyl sulfonic acid. Itis preferable to use acrylate rubber homo- or copolymers which containfrom 0.01 to 8 wt. % of divinyl or polyvinyl compounds and/orN-methylolacrylamide or N-methylolmethacrylamide or other compoundsacting as crosslinking agents, for example divinylbenzene,triallylcyanurate.

Polybutadiene rubbers, SBR rubbers with up to 30 wt. % of styreneincorporated by polymerisation and acrylate rubbers, in particular thosehaving a core/shell structure, for example as described in DE-OS 3 006804, are preferred.

Latices having average particle diameters d₅₀ of 0.05 to 2.0 μm,preferably of 0.08 to 1.0 μm and particularly preferably of 0.1 to 0.5μm can be used for producing the graft polymers according to theinvention. The gel contents of the rubbers used can be varied in widelimits and preferably lie between 30 and 95 wt. % (determined by thewire cage method in toluene (cf. Houben-Weyl, Methoden der OrganischenChemie, Makromolekulare Stoffe, part 1, page 307 (1961) Thieme VerlagStuttgart)).

Quite particularly preferred are mixtures of rubber latices having

a) average particle diameters d₅₀≦320 nm, preferably 260 to 310 nm, andgel contents ≦70 wt. %, preferably 40 to 65 wt. % and

b) average particle diameters d₅₀≧370 nm, preferably 380 to 450 nm, andgel contents ≦70 wt. %, preferably 75 to 90 wt. %.

The rubber latex (a) preferably has a particle size distribution rangeof 30 to 100 nm, particularly preferably of 40 to 80 nm, and the rubberlatex (b) of 50 to 500 nm, particularly preferably of 100 to 400 nm(measured as d₉₀-d₁₀ value from the integral particle size distributionin each case).

The mixtures contain the rubber latices (a) and (b) preferably in aratio by weight of 90:10 to 10:90, particularly preferably 60:40 to30:70 (based on the respective solids content of the latices in eachcase).

The average particle diameters are determined by ultracentrifuge (cf. W.Scholtan, H. Lange: Kolloid-Z. u Z. Polymere 250, pages 782 to 796(1972).

The values given for the gel content are determined by the wire cagemethod in toluene (cf. Houben-Weyl, Methoden der Organischen Chemie,Makromolekulare Stoffe, part 1, page 307 (1961) Thieme VerlagStuttgart).

The rubber latices used can be produced by emulsion polymerisation andthe necessary reaction conditions, auxiliaries and production techniquesare basically known.

It is also possible initially to produce a finely divided rubber polymerby known methods and then to agglomerate it in a known manner to adjustthe necessary particle size. Appropriate techniques are described (cf.EP-PS 0 029 613; EP-PS 0 007 810; DD-PS 144 415; DE-AS 12 33 131; DE-AS12 58 076; DE-OS 21 01 650; U.S. Pat, No. 1,379,391).

The so-called seed polymerisation technique can also be employed, duringwhich, for example, a finely divided butadiene polymer is initiallyproduced and is then repolymerised to larger particles by subsequentreaction with butadiene-containing monomers.

Conventional anionic emulsifiers such as alkyl sulfates, alkylsulfonates, aralkyl sulfonates, soaps of saturated or unsaturated fattyacids (for example oleic acid, stearic acid) as well as alkalinedisproportionated or hydrogenated abietic acid or talloleic acid can beused as emulsifiers, emulsifiers containing a carboxyl group (forexample salts of C₁₀-C₁₈ fatty acids, disproportionated abietic acid)preferably being used.

Rubber polymer latices can basically also be produced by emulsificationof finished rubber polymers in aqueous media (cf. Japanese patentapplication 55 125 102).

Graft monomers which are polymerised in the presence of the rubber-likepolymers existing in the form of an emulsion include virtually allcompounds which can be polymerised in an emulsion to thermoplasticresins, for example vinyl aromatic substances corresponding to formula(I) or compounds corresponding to formula (II) or mixtures thereof

in which

R¹ represents hydrogen or methyl,

R² represents hydrogen, halogen or alkyl containing 1 to 4 carbon atomsin the ortho-, meta- or para-position,

R³ represents hydrogen or methyl and

X represents CN, R⁴OOC or R⁵R⁶NOC, wherein

R⁴ represents hydrogen or alkyl containing 1 to 4 carbon atoms; and

R⁵ and R⁶ independently represent hydrogen, phenyl or alkyl containing 1to 4 carbon atoms.

Examples of compounds corresponding to formula (I) include styrene,α-methyl styrene, p-methyl styrene and vinyltoluene. Compoundscorresponding to formula (II) include acrylonitrile and methylmethacrylate. Further monomers which are basically suitable include forexample, vinyl acetate and N-phenylmaleimide.

Preferred monomers are mixtures of styrene and acrylonitrile, α-methylstyrene and acrylonitrile, of styrene, acrylonitrile and methylmethacrylate as well as combinations of these monomer mixtures withN-phenylmaleimide.

Preferred graft polymers A) according to the invention are thoseobtained by graft polymerisation of styrene and acrylonitrile in a ratioby weight of 90:10 to 50:50, preferably 80:20 to 65:35 (wherein styrenecan be completely or partially replaced by α-methyl styrene or methylmethacrylate) in the presence of quantities of rubber, preferablypolybutadiene, which are sufficient to produce graft polymers havingrubber contents of 20 to 80 wt. %, preferably 30 to 75 wt. % andparticularly preferably 35 to 70 wt. %.

The graft polymers A) are produced according to the invention in that aredox initiator system is added to the rubber latex or the rubber latexmixture at the beginning of the grafting reaction.

Suitable redox initiator systems generally consist of an organicoxidising agent and a reducing agent, heavy metal ions preferablyadditionally being present in the reaction medium.

Organic oxidising agents which are suitable according to the inventioninclude, for example, di-tert.-butylperoxide, cumene hydroperoxide,dicyclohexylpercarbonate, tert.-butylhydroperoxide, p-methanehydroperoxide, cumene hydroperoxide and tert.-butylhydroperoxide beingpreferred. H₂O₂ can basically also be used.

Reducing agents which can be used according to the invention arepreferably water-soluble compounds, for example salts of sulfinic acid,salts of sulfuric acid, sodium dithionite, sodium sulfite, sodiumhyposulfite, sodium hydrogen sulfite, ascorbic acid and salts thereof,Rongalite C (sodium formaldehyde sulfoxylate), mono- anddihydroxyacetone, sugar (for example glucose or dextrose), iron(II)salts, such as, for example iron(II) sulfate, tin(II) salts, such as,for example tin(II) chloride, titanium(III) salts such as titanium(III)sulfate.

Preferred reducing agents include water-soluble compounds, for exampledextrose, ascorbic acid (salts) or sodium formaldehyde sulfoxylate(Rongalite C).

The quantities of oxidising agent used are from 0.05 to 2.0 wt. %,preferably 0.1 to 1.5 wt. % and particularly preferably 0.2 to 1.2 wt.%. Reducing agents are used in quantities of 0.05 to 1.5 wt. %,preferably of 0.08 to 1.2 wt. % and particularly preferably of 0.1 to1.0 wt. % (based on the monomers added up to the moment of addition ofpersulfate compound in each case).

The graft monomers are subsequently added and, after a quantity of 10 to95 wt. %, preferably 20 to 85 wt. %, particularly preferably 20 to 80wt. %, in particular 30 to 75 wt. % and quite particularly preferably 35to 70 wt. % has been added (based on total quantity of monomers in eachcase), at least one persulfate compound is added in quantities of 0.05to 1.5 wt. %, preferably 0.08 to 1.2 wt. % and particularly preferably0.1 to. 1.0 wt. % (based on the monomers added from the beginning ofaddition of persulfate compound in each case).

Suitable persulfate compounds include, for example, sodiumperoxodisulfate, potassium peroxodisulfate, ammonium peroxodisulfate,potassium peroxodisulfate being the preferred persulfate compound.

The redox initiator components as well as the persulfate compound areconventionally used in the form of aqueous solutions, aqueous emulsions,aqueous suspensions or other aqueous dispersions. The remaining monomersare then added and completely polymerised.

The invention also provides a process for producing graft rubbers byemulsion polymerisation using a combination of initiators consisting ofa redox initiator system and a persulfate compound, wherein

i) the graft monomers are added to the rubber latex,

ii) the redox initiator components are added in quantities of 0.1 to 2.5wt. % (based on the monomers added up to the moment of addition ofpersulfate compound) at the beginning of the graft polymerisationreaction,

iii) a persulfate compound is added in quantities of 0.05 to 1.5 wt. %(based on the monomers added from the moment of addition of thepersulfate compound) after a monomer addition of 10 to 95 wt. % (basedon total quantity of monomers) and

iv) the polymerisation reaction is completed.

The reaction temperature during production of the graft rubbers A)according to the invention can be varied within wide limits. It is from25° C. to 160° C., preferably 40° C. to 90° C. The temperature at thebeginning of monomer addition quite particularly preferably differs fromthe temperature at the end of monomer addition by a maximum of 20° C.,preferably a maximum of 10° C. and particularly preferably a maximum of5° C.

Molecular weight regulators can additionally be used during graftpolymerisation, preferably in quantities of 0.05 to 2 wt. %,particularly preferably in quantities of 0.1 to 1 wt. % (based on totalquantity of monomer in each case).

A procedure which is preferred according to the invention involves theaddition of molecular weight regulators only in the portion of thereaction after addition of the persulfate compound and the avoidance ofregulator addition in the portion of the reaction prior to addition ofthe persulfate compound.

Suitable molecular weight regulators include, for example,n-dodecylmercaptan, t-dodecylmercaptan, dimeric α-methyl styrene,terpinolene and combinations of mixtures of these compounds.

The above-mentioned compounds can be used as emulsifiers during thegraft polymerisation reaction.

The graft rubber latex A) is worked up by known processes, for exampleby spray drying or by addition of salts and/acids, washing of theprecipitates and drying of the powder.

Copolymers of styrene and acrylonitrile are preferably used as vinylresins B) in a proportion by weight of 90:10 to 50:50, wherein styreneand/or acrylonitrile can be completely or partially replaced by α-methylstyrene and/or methyl methacrylate; a proportion of up to 30 wt. %(based on vinyl resin) of a further monomer from the range comprisingmaleic anhydride, maleimide, N-(cyclo) alkylmaleimide,N-(alkyl)-phenylmaleimide can optionally also be used.

The average molecular weights ({overscore (M)}_(w)) of these resins canbe varied in wide limits and they preferably lie between about 40,000and 200,000, particularly preferably between 50,000 and 150,000.

Details concerning the production of these resins are provided, forexample, in DE-AS 2 420 358 and DE-AS 2 724 360. Resins produced by massand solution polymerisation and by suspension polymerisation have provenparticularly suitable.

The proportion of the elastic/thermoplastic graft polymer (A) in themoulding composition according to the invention can be varied in widelimits; it is preferably 10 to 80 wt. %, particularly preferably 20 to75 wt. %.

The necessary or advantageous additives, for example antioxidants, UVstabilisers, peroxide destroyers, antistatic agents, lubricants, mouldrelease agents, flameproofing agents, fillers or reinforcing agents(glass fibres, carbon fibres, etc.) and colourants can be added to themoulding compositions according to the invention during production,working up, further processing and final shaping.

Final shaping can be carried out on conventional commercial processingunits and involves, for example, injection moulding, sheet extrusionoptionally with subsequent thermal shaping, cold shaping, extrusion ofpipes and profiles or calendering.

The moulding compositions according to the invention of the ABS type canbe blended with other polymers. Suitable blending partners are selected,for example, from at least one polymer selected from the groupcomprising polycarbonates, polyesters, polyester carbonates andpolyamides.

Suitable thermoplastic polycarbonates and polyester carbonates are known(cf., for example, DE-AS 1 495 626, DE-OS 2 232 877, DE-OS 2 703 376,DE-OS 2 714 544, DE-OS 3 000 610, DE-OS 3 832 396, DE-OS 3 077 934), forexample can be produced by reaction of diphenols corresponding to theformulae (III) and (IV)

wherein

A is a simple bond, C₁-C₅ alkylene, C₂-C₅ alkylidene, C₅-C₆cycloalkylidene, —O—, —S—, —SO—, —SO₂— or —CO—,

R⁷ and R⁸ independently represent hydrogen, methyl or halogen, inparticular hydrogen, methyl, chlorine or bromine,

R⁹ and R¹⁰ independently represent hydrogen, halogen, preferablychlorine or bromine, C₁-C₈ alkyl, preferably methyl, ethyl, C₅-C₆cycloalkyl, preferably cyclohexyl, C₆-C₁₀ aryl, preferably phenyl, orC₇-C₁₂ aralkyl, preferably phenyl-C₁-C₄ alkyl, in particular benzyl,

m is an integer from 4 to 7, preferably 4 or 5,

n is 0 or 1,

R¹¹ and R¹² can be selected individually for each X and independentlyrepresent hydrogen or C₁-C₆ alkyl and

X′ represents carbon,

with carbonyl halides, preferably phosgene, and/or with aromaticdicarboxylic acid dihalides, preferably benzene dicarboxylic aciddihalides, by phase interface polycondensation or with phosgene bypolycondensation in the homogeneous phase (the so-called pyridineprocess), wherein the molecular weight can be adjusted in a known mannerby an appropriate quantity of known chain terminators.

Suitable diphenols corresponding to formulae (III) and (IV) include, forexample, hydroquninone, resorcinol, 4,4′-dihydroxydiphenyl,2,2,-bis-(4-hydroxyphenyl)-propane,2,4-bis-(4-hydroxyphenyl)-2-methylbutane,2,2-bis-(4-hydroxy-3,5-dimethylphenyl)-propane,2,2-bis-(4-hydroxy-3,5-dichlorophenyl)-propane,2,2-bis-(4-hydroxy-3,5-dibromophenyl)-propane,1,1-bis-(4-hydroxyphenyl)-cyclohexane,1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,1,1-bis-(4-hydroxyphenyl)-3,3-dimethylcyclohexane,1,1-bis-(4-hydroxyphenyl)-3,3,5,5-tetramethylcyclo-hexane or 1,1-bis-(4-hydroxyphenyl)-2,4,4,-trimethylcyclopentane.

2,2-bis-(4-hydroxyphenyl)-propane and1,1-bis-(4-hydroxyphenyl)-cyclohexane are preferred diphenolscorresponding to formula (III) and1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane is the preferredphenol corresponding to formula (IV).

Mixtures of diphenols can also be used.

Suitable chain terminators include, for example, phenol, p-tert.-butylphenol, long-chained alkyl phenols such as4-(1,3-tetramethyl-butyl)phenol according to DE-OS 2 842 005, monoalkylphenols, dialkyl phenols with a total of 8 to 20 carbon atoms in thealkyl substituents according to DE-OS 3 506 472 such as p-nonyl phenol,2,5-di-tert.-butyl phenol, p-tert.-octyl phenol, p-dodecyl phenol,2-(3,5-dimethylheptyl)-phenol and 4-(3,5-dimethylheptyl)-phenol. Thequantity of chain terminators required is generally from 0.5 to 10 mole%, based on the sum of diphenols (I) and (II).

Suitable polycarbonates and polyester carbonates can be linear orbranched; branched products are preferably obtained by incorporatingfrom 0.05 to 2.0 mole %, based on the sum of diphenols used, oftrifunctional or higher than trifunctional compounds, for example thosewith three or more than three phenolic OH groups.

Suitable polycarbonates and polyester carbonates can containaromatically bound halogen, preferably bromine and/or chlorine; they arepreferably halogen-free.

They have average molecular weights ({overscore (M)}_(w), weightaverage) determined, for example, by ultracentrifugation or scatteredlight measurement of 10,000 to 200,000, preferably 20,000 to 80,000.

Suitable thermoplastic polyesters are preferably polyalkyleneterephthalates, i.e. reaction products of aromatic dicarboxylic acids orreactive derivatives thereof (for example dimethylesters or anhydrides)and aliphatic, cycloaliphatic or arylaliphatic diols and mixtures ofthese reaction products.

Preferred polyalkylene terephthalates can be produced from terephthalicacids (or reactive derivatives thereof) and aliphatic or cycloaliphaticdiols containing 2 to 10 carbon atoms by known methods(Kunststoff-Handbuch, Volume VIII, page 695 et seq., Carl Hanser Verlag,Munich 1973).

In preferred polyalkylene terephthalates, 80 to 100, preferably 90 to100 mole % of the dicarboxylic acid radicals are terephthalic acidradicals and 80 to 100, preferably 90 to 100 mole % of the diol radicalsare ethyleneglycol and/or butanediol-1,4-radicals.

In addition to ethyleneglycol and butanediol-1,4-radicals, the preferredpolyalkylene terephthalates can contain from 0 to 20 mole % of radicalsof different aliphatic diols containing from 3 to 12 carbon atoms orcycloaliphatic diols containing from 6 to 12 carbon atoms, for exampleradicals of propanediol-1,3,2-ethylpropanediol-1,3, neopentylglycol,pentanediol-1,5, hexanediol-1,6,cyclohexandimethanol-1,4,3-methylpentanediol-1,3, and-1,6,2-ethylhexanediol-1,3,2,2,-diethylpropanediol-1,3,hexanediol-2,5,1,4-di(β-hydroxyethoxy)-benzene,2,2,-bis-4-hydroxycyclohexyl)-propane,2,4-dihydroxy-1,1,3,3-tetramethylcyclobutane,2,2-bis-(3-β-hydroxyethoxyphenyl)-propane and2,2-bis-(4-hydroxypropoxyphenyl)-propane (DE-OS 2 407 647, 2 407 776, 2715 932).

The polyalkylene terephthalates can be branched by incorporation ofrelatively small quantities of trihydric or tetrahydric alcohols ortribasic or tetrabasic carboxylic acids of the type described in DE-OS 1900 270 and U.S. Pat. No. 3,692,744. Examples of preferred branchingagents include trimesic acid, trimellitic acid, trimethylolethane andpropane and pentaerythritol. It is advisable to use not more than 1 mole% of the branching agent, based on the acid component.

Polyalkylene terephthalates produced solely from terephthalic acid andthe reactive derivatives thereof (for example the dialkyl estersthereof) and ethyleneglycol and/or butanediol-1,4 and mixtures of thesepolyalkylene terephthalates are particularly preferred.

Preferred polyalkylene terephthalates also include copolyesters producedfrom at least two of the above-mentioned alcohol components:poly-(ethyleneglycolbutanediol-1,4)-terephthalates are particularlypreferred copolyesters.

The preferred polyalkylene terephthalates generally have an intrinsicviscosity of 0.4 to 1.5 dl/g, preferably 0.5 to 1.3 dl/g, in particular0.6 to 1.2 dl/g measured in phenol/o-dichlorobenzene (1:1 parts byweight) at 25° C. in each case.

Suitable polyamides include known homopolyamides, copolyamides andmixtures of these polyamides. These can be partially crystalline and/oramorphous polyamides.

Polyamide-6, polyamide-6,6, mixtures and corresponding copolymers ofthese components are suitable as partially crystalline polyamides.Partially crystalline polyamides of which the acid component consistscompletely or partially of terephthalic acid and/or isophthalic acidand/or suberic acid and/or sebacic acid and/or azelaic acid and/oradipic acid and/or cyclohexane dicarboxylic acid, of which the diaminecomponents consist completely or partially of m- and/orp-xylylenediamine and/or hexamethylenediamine and/or2,2,4-trimethylhexamethylelendiamine and/or2,2,4-trimethylhexamethylenediamine and/or isophoronediamine and ofwhich the composition is basically known can also be used.

Polyamides which are produced completely or partially from lactams with7 to 12 carbon atoms in the ring should also be mentioned, optionallywhile using one or more of the above-mentioned starting components.

Polyamide-6 and polyamide-6,6 and mixtures thereof are particularlypreferred partially crystalline polyamides. Known products can be usedas amorphous polyamides. They are obtained by polycondensation ofdiamines such as ethylenediamine, hexamethylenediamine,decamethylenediamine, 2,2,4- and/or 2,4,4-trimethylhexamethylenediamine,m- and/or p-xylylene-diamine, bis-(4-aminocyclohexyl)-methane,bis-(4-aminocyclohexyl)-propane,3,3′-dimethyl-4,4′-diamino-dicyclohexylmethane,3-aminomethyl-3,5,5,-trimethylcyclohexylamine, 2,5- and/or2,6-bis-(aminomethyl)-norbornane and/or 1,4-diaminomethylcyclohexanewith dicarboxylic acids such as oxalic acid, adipic acid, azelaic acid,decanedicarboxylic acid, heptadecanedicarboxylic acid, 2,2,4- and/or2,4,4-trimethyladipic acid, isophthalic acid and terephthalic acid.

Copolymers obtained by polycondensation of several monomers are alsosuitable, moreover copolymers produced by addition of aminocarboxylicacids such as ε-aminocaproic acid, ω-aminoundecanic acid orω-aminolauric acid or lactams thereof.

Particularly suitable amorphous polyamides include polyamides producedfrom isophthalic acid, hexamethylenediamine and other diamines such as4,4′-diaminodicyclohexylmethane, isophoronediamine, 2,2,4- and/or2,4,4-trimethylhexamtheylenediamine, 2,5- and/or2,6-bis-(aminomethyl)-norbornene, or from isophthalic acid,4,4′-diamino-dicyclohexylmethane and ε-caprolactam; or from isophthalicacid, 3,3′-dimethyl-4,4′-diamino-dicyclohexylmethane and laurinlactam;or from terephthalic acid and the isomer mixture of 2,2,4- and/or2,4,4-trimethylhexamethylenediamine.

Instead of pure 4,4′-diaminodicyclohexylmethane, it is also possible touse mixtures of the positional isomeric diaminodicyclohexylmethanescomposed of

70 to 99 mole % of the 4,4′-diamino-isomer

1 to 30 mole % of the 2,4′-diamino-isomer

0 to 2 mole % of the 2,2′-diamino-isomer and

optionally correspondingly more highly condensed diamines obtained byhydrogenation of industrial quality diaminodiphenylmethane. Up to 30% ofthe isophthalic acid can be replaced by terephthalic acid.

The polyamides preferably have a relative viscosity (measured on a 1 wt.% solution in m-cresol at 25° C.) of 2.0 to 5.0, particularly preferably2.5 to 4.0.

If at least one polymer selected from the group comprisingpolycarbonates, polyesters, polyester carbonates and polyamides isadditionally used, the quantity thereof is up to 500 parts by weight,preferably up to 400 parts by weight and particularly preferably up to300 parts by weight (based on 100 parts by weight A+B in each case).

In the following examples, the parts mentioned are always parts byweight and the % mentioned always wt. % unless otherwise stated.

EXAMPLES Example 1

According to the Invention

60 parts by weight (calculated as solid material) of a polybutadienelatex mixture (50% with an average particle diameter d₅₀ of 421 nm and agel content of 85 wt. % and 50% with an average particle diameter d₅₀ of276 nm and a gel content of 47 wt. %, both produced by radicalpolymerisation) are brought to a solids content of about 20 wt. % withwater and are then heated to 63° C. Initially 0.045 parts by weight ofsodium ascorbate (in the form of an aqueous solution) and then 0.135parts by weight of tert.-butylhydroperoxide are subsequently added whilestirring.

20 parts by weight of a monomer mixture consisting of 73 wt. % ofstyrene and 27 wt. % of acrylonitrile and 0.06 parts by weight oftert.-dodecylmercaptan are then added uniformly within 2 h.

0.25 parts by weight of potassium peroxodisulfate (dissolved in water)are then added and 20 parts by weight of a monomer mixture consisting of73 wt. % of styrene and 27 wt. % of acrylonitrile and 0.06 parts byweight of tert.-dodecylmercaptan are then added uniformly within 2 h.

Simultaneously with the monomers, 1 part by weight (calculated as solidsubstance) of the sodium salt of a resinic acid mixture (Dresinate 731,Abieta Chemie GmbH, Gersthofen, dissolved in alkaline water) is addedover 4 hours.

After a post-reaction time of 4 hours, the graft latex is coagulated,after addition of about 1 part by weight of a phenolic antioxidant, witha magnesium sulfate/acetic acid mixture, and the resultant powder driedunder vacuum at 70° C. after washing with water. 40 parts by weight ofthis graft polymer are blended with 60 parts by weight of astyrene/acrylonitrile copolymer resin (72:28, M_(w)≈15 000,M_(w)/M_(n)−1≦2),

2 parts by weight of ethylenediamine bisstearylamide and 0.1 part byweight of a silicone oil are blended in an internal kneader andsubsequently processed into test pieces.

The Following Data Have Been Determined

Notched impact strength at room temperature (a_(k) ^(RT)) and at −40° C.(a_(k) ^(−40° C.)) according to ISO 180/1A (unit: kJ/m²),

ball indentation hardness (H_(c)) according to DIN 53 456 (unit: N/mm²);

The thermoplastic flowability was assessed by measuring the necessaryinjection pressure at 240° C. (unit:bar) (see F. Johannaber, Kunststoffe74 (1984), 1, pages 2 to 5);

The crude shade (colour in the undyed state) was assessed visually inthe classifications

++ very light

+ light

o medium

− dark

−− very dark

The results are shown in Table 1.

Example 2

According to the Invention

Example 1 is repeated except that tert.-dodecylmercaptan is added in aquantity of 0.12 parts by weight together with the monomers afteraddition of potassium peroxodisulfate.

Example 3

Comparison

Example 1 is repeated except that 0.25 parts by weight of potassiumperoxodisulfate (dissolved in water) are added after heating the rubberlatex mixture rather than adding sodium ascorbate andtert.-butylhydroperoxide.

Example 4

Comparison

Example 1 is repeated except that 0.25 parts by weight of potassiumperoxodisulfate (dissolved in water) are added instead of the additionof sodium ascorbate and tert.-butylhydroperoxide after heating therubber latex mixture and 0.045 parts by weight of sodium ascorbate(aqueous solution) and 0.135 parts by weight of tert.-butylhydroperoxideare added instead of the addition of potassium peroxodisulfate, afteradding monomers for two hours.

Example 5

According to the Invention

60 parts by weight (calculated as solid material) of an anionicallyemulsified polybutadiene latex produced by radical polymerisation with aparticle diameter d₅₀ of 421 nm and gel content of 85 wt. % are adjustedto a solids content of about 20 wt. % with water and then heated to 63°C. The grafting reaction is then carried out in the manner described inExample 1.

Example 6

Comparison

Example 5 is repeated using the procedure described in Example 3.

Example 7

According to the Invention

50 parts by weight (calculated as solid material) of a rubber latex,obtained from a basic latex having an average particle diameter d₅₀ of98 nm by chemical agglomeration, with an average particle diameter d₅₀of 276 nm and a gel content of 93 wt. % are adjusted to a solids contentof about 25 wt. % by addition of water and then heated to 58° C.Initially 0.2 parts by weight of dextrose and 0.004 parts by weight ofiron(II) sulfate (in the form of an aqueous solution in each case) andthen 0.125 parts by weight of cumene hydroperoxide (in the form of anaqueous emulsion) are subsequently added while stirring.

30 parts by weight of a monomer mixture of 70 wt. % of styrene and 30wt. % of acrylonitrile and 0.27 parts by weight oftert.-dodecylmercaptan are then added uniformly within 1.5 h.

0.25 parts by weight of potassium peroxodisulfate (dissolved in water)are then added and 20 parts by weight of a monomer mixture of 70 wt. %of styrene and 30 wt. % of acrylonitrile and 0.28 parts by weight oftert.-dodecylmercaptan are then added uniformly within 1.5 h.

After a post-reaction time of 3 hours, the graft latex is coagulatedwith a magnesium sulfate solution after addition of about 1.5 parts byweight of an antioxidant and the resultant powder dried under vacuum at70° C. after washing with water.

40 parts by weight of the graft polymer are blended with 60 parts byweight of a styrene/acrylonitrile copolymer resin (72:28, {overscore(M)}_(w)≈138 000),

1 part by weight of pentaerythritol tetrastearate and 0.15 parts byweight of a silicone oil are blended in an internal kneader and are thenprocessed into test pieces.

Example 8

Comparison

Example 7 is repeated using a procedure similar to that in Example 3.

It can be seen from the test values compiled in Table 1 that only themoulding compositions according to the invention exhibit an increase inviscosity without adversely affecting rigidity and processibility.

Very good crude shade values are also achieved.

TABLE 1 Test data of investigated moulding compositions Ignition a_(k)^(RT) a_(k) ^(−40° C.) H_(c) pressure Crude Example (kJ/m²) (kJ/m²)(N/mm²) (bar) shade 1 44 30 82 174 + 2 46 30 83 166 ++ 3 (comparison) 3826 82 159 − 4 (comparison) 38 28 81 170 ∘ 5 48 30 82 175 ++ 6(comparison) 43 26 83 168 − 7 36 14 93 210 + 8 (comparison) 28 10 93 205−

What is claimed is:
 1. A thermoplastic ABS moulding compositioncomprising: A) at least one elastic/thermoplastic graft polymer preparedby radical emulsion polymerisation of resin-forming vinyl monomers inthe presence of rubber existing in latex form with a glass transitiontemperature ≦0° C. using an initiator combination consisting of a redoxinitiator system and a persulfate compound; and B) at least onecopolymer composed of styrene and acrylonitrile and optionally furthercomonomers, wherein graft polymer A) is produced by the steps of, (i)supplying a portion of the vinyl monomers to the rubber latex, (ii)adding the redox initiator components at the beginning of the graftpolymerisation reaction in quantities of 0.1 to 2.5 wt. % (based on themonomers added up to the moment of addition of persulfate compound ineach case), (iii) adding said persulfate compound after an addition ofmonomers of 10 to 95 wt. % (based on total quantity of monomer in eachcase), in quantities of 0.05 to 1.5 wt. % (based on the monomers addedfrom the moment of addition of persulfate compound in each case), and(iv) allowing polymerisation to proceed to completion, further whereinthe rubber existing in latex form of graft polymer A) is a mixture of atleast two rubber latices having, a) an average particle diameter d₅₀≦320nm and a gel content ≦70 wt. %, and b) an average particle diameterd₅₀≧370 nm, and a gel content ≧70 wt. %.
 2. The thermoplastic mouldingcomposition of claim 1 wherein graft polymer A) is present in quantitiesof 10 to 80 wt. %.
 3. The thermoplastic moulding composition of claim 1wherein the elastic/thermoplastic graft polymer A) has a rubber contentof 20to 80 wt. %.
 4. The thermoplastic moulding composition of claim 1wherein styrene and acrylonitrile are used as resin-forming monomersduring the production of graft polymer A).
 5. The thermoplastic mouldingcomposition of claim 1 wherein the redox initiator system for producinggraft polymer A) comprises (i′) an oxidixing component selected from atleast one of cumene hydroperoxide and tert.-butylhydroperoxide, and(ii′) a reducing component selected from at least one of dextrose,ascorbic acid, ascorbic acid salt and sodium formaldehyde sulfoxylate.6. The thermoplastic moulding composition of claim 1 wherein potassiumperoxodisulfate is used as persulfate compound for producing graftpolymer A).
 7. The thermoplastic moulding composition of claim 1 whereincopolymer B) is made up of monomers selected from styrene, α-methylstyrene, acrylonitrile, methyl methacrylate, maleic anhydride,N-phenylmaleimide and mixtures thereof.
 8. The thermoplastic mouldingcomposition of claim 1, additionally comprising at least one resinselected from the group consisting of polycarbonates, polyestercarbonates, polyesters and polyamides.
 9. A molded article comprisingthe composition of claim
 1. 10. The moulding composition of claim 1wherein during the production of graft polymer A), polymerisation takesplace before addition of the persulfate compound in the absence ofmolecular weight regulator, and polymerisation takes place afteraddition of the persulfate compound in the presence of molecular weightregulator.
 11. A process for producing rubber-containing graft polymersby emulsion polymerisation using a combination of initiators consistingof a redox initiator system and a persulfate compound, said processcomprising the steps of: i) adding graft monomers to a rubber latex, ii)adding redox initiator components in quantities of 0.1 to 2.5 wt. %(based on the monomers added up to the moment of addition of persulfatecompound) at the beginning of the graft polymerisation reaction, iii)adding said persulfate compound in quantities of 0.05 to 1.5 wt. %(based on the monomers added from the moment of addition of thepersulfate compound) after a monomer addition of 10 to 95 wt. % (basedon total quantity of monomers); and iv) allowing the polymerisationreaction to proceed to completion, wherein said rubber latex of step i)is a mixture of at least two rubber latices having, a) an averageparticle diameter d₅₀≦320 nm and a gel content ≦70 wt. %, and b) anaverage particle diameter d₅₀≧370 nm, and a gel content ≧70 wt. %. 12.The process of claim 11 wherein during said process, polymerisationtakes place before addition of the persulfate compound in the absence ofmolecular weight regulator, and polymerisation takes place afteraddition of the persulfate compound in the presence of molecular weightregulator.
 13. A thermoplastic ABS moulding composition containing: A)at least one elastic/thermoplastic graft polymer prepared by radicalemulsion polymerisation of resin-forming vinyl monomers in the presenceof rubber existing in latex form with a glass transition temperature ≦0°C. using an initiator combination consisting of a redox initiator systemand a persulfate compound; and B) at least one copolymer composed ofstyrene and acrylonitrile and optionally further comonomers, whereingraft polymer A) is produced by the steps of, (i) supplying a portion ofthe vinyl monomers to the rubber latex, (ii) adding the redox initiatorcomponents at the beginning of the graft polymerisation reaction inquantities of 0.1 to 2.5 wt. % (based on the monomers added up to themoment of addition of persulfate compound in each case), (iii) adding apersulfate compound after an addition of monomers of 10 to 95 wt. %(based on total quantity of monomer in each case), in quantities of 0.05to 1.5 wt. % (based on the monomers added from the moment of addition ofpersulfate compound in each case), and (iv) allowing polymerisation toproceed to completion, further wherein during the production of graftpolymer A), polymerisation takes place before addition of the persulfatecompound in the absence of molecular weight regulator, andpolymerisation takes place after addition of the persulfate compound inthe presence of molecular weight regulator.
 14. A process for producingrubber-containing graft polymers by emulsion polymerisation using acombination of initiators consisting of a redox initiator system and apersulfate compound, said process comprising the steps of: i) addinggraft monomers to a rubber latex, ii) adding redox initiator componentsin quantities of 0.1 to 2.5 wt. % (based on the monomers added up to themoment of addition of persulfate compound) at the beginning of the graftpolymerisation reaction, iii) adding said persulfate compound inquantities of 0.05 to 1.5 wt. % (based on the monomers added from themoment of addition of the persulfate compound) after a monomer additionof 10 to 95 wt. % (based on total quantity of monomers); and iv)allowing the polymerisation reaction to proceed to completion, whereinduring said process, polymerisation takes place before addition of thepersulfate compound in the absence of molecular weight regulator, andpolymerisation takes place after addition of the persulfate compound inthe presence of molecular weight regulator.